Electrical instrument



April 1933- aiw. s'r. CLAIR 1,904,096

ELECTRICAL INSTRUMENT Filed Jan. 19, 1932 Inventor:

Byron V\/. StClah by His Attovneg.

.Patentod 1933,

jjnnou er.

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march; msrnmm Application fled Ian-nary 19, 1932. Serial Io. 557,597.

My invention relates to electrical instruments and concerns articularlyinstruments in which the zero and the lower portion ofthe scale aresuppressed.

The principal object of my invention is to provide a simple reliablearrangement in. which the zero suppression is eflected electri cally,thereb eliminating strains or violent stresses whic might injure theinstrument or alter the calibration when the measured value remains ator tells suddenly to a low value, ()ther objects will become apparentcsthe description proceeds.

in the usual form of new sugpression restraining springs are utilised.However, the stresses set upon the springs tend to cause serious errorsin thecourse or? time, This diillculty is overcome, in accordance withmy invention, by supplying the restraining force electrically.

A diiderentisl type of instrument or one in which one of the'windingsmay be divided into two-opposing portions is arranged so that the opsing windings are traversed by subwe stsntie 1y balanced currents untilthe measured quantity etteins e value eorrespondingto e point at thelower end of the scale rungs. When the meesured quantity exceeds thisvalue the current treversing one of the windings increases less rs idlyor becomes substantiully constant as t e current in the other windingcontinues to increase in response to an increase in the magnitude of themeesured qusntity. This result may be accomplished by connectin one oithe instrument Windmeesured in series wit the primary veindi of atransformer, and connecting the other winding of the instrument to thesecondary oi the trensiormenwhich is so desi ed that its magnetic coresaturates for a v us of the measured quantity at the lower end of theinstrument ran e. The features of my invention which Iielieve to benovel and patentable are pointed out in the claimsappended hereto.

In the accompanyinidrawin which 1llus-. trates my invention t ere is sown an arrangement for measuring voltage across'tho points 11 and 12 ofan alternating-current circuit but it will be understood that apparatusarranged in accordance with my invention may be applied to themeasurement of other quantities as Well. A suitable electricalinstrument or current responsive device 13 is provided havingdifierential or opposed windin s 1d and 15, and e pointer 16 cooperstingwith a scale 17. A transformer 18 has a primary winding 19 connected inseries with instrument winding 15 and resistance or multiplier 2d ecrosspoints 11 end 12 of en alternating-current circuit between which voltageis to be measured. The secondary windin 21 of transformer 18 isconnected to win ing it of instrument 13.

For volteges ebove e predetermined value the core 22 oi trensiormei- 18becomes megneticelly sstureted end the current in instrument windin 14remains substantially constant, elthougi 15 continues to increase withincrease in volt-= ego. Preferably windings it end 15 are belencedwindings, end transformer 18 has substentielly on equal number oi-turnsto 've n 1:1 ratio: but obviously 1' sin not limited to this exacterrengernent. if, for example, the device is designed to have on exended scele over the renge of 100 to 150 V0 ts, the transformer 18 wouldbe designed to seturete at approximately 100 volts so that thedeflection oi pointer 16 would be negligible for voltages under 100.Although I have shown on indicating illustration it will be understoodthat my invention is not limited thereto but obviously includes allcurrent responsive or measuring a specific manner in accordance with theprovisionsof the patent statutes, it should be the current in winding tvoltmeter by way of w'attmeters,

mg devices having current or potential windings understood that I do notlimit my invention thereto since various modifications thereof willsuggest themselves to those skilled in the. art without departingfromthespirit of my invention, thescope of which is set forth in theappended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is:

1. In combination with an alternatingcurrent circuit, a transformerhaving primary and secondary windings and an electrical measuring devicehaving a winding divided into two opposing portions, said-transformerprimary and one portion oi the winding oi said measuring device inseries being connected to said alternating-current circuit saidtransformer secondary being connected to the other portion of thewinding of said 35 measuring device.

2. in combination with an alternating" current circuit, a transformerhaving primary and secondary windings, and a voltmeter having' a pair ofopposing field windings, said transtormer primary and one of said fieldwindings in series bemg connected to said alternating-current circuit,said transformer mcondary being connected to the other of said voltmeter.1eld windings.

3. A. suppressed zero measuring device 1 comprising in combination withan alternating-current system, an electrical instrument having a windingdivided into two opposing portions, a transformer having a core ofmagnetic material, and primary and secondary windings, said transformerprimary and one pgrtlon of said instrument winding miseries mg connectedto said alternating-current system, said transformer secondary beingconnected to the other portion of said instrument winding, therelationship between the electrical and magnetic circuits of thetransformer bein such that for measured values below a point in thelower portion of the range of the device the transformer core isrelatively unsaturated and for measured values within the range of thedevice, the transformer core becomes saturated.

4. A suppressed zero voltmeter comprising in combination with analternating-current system, an electrical instrument having a pair ofopposing field windings, a transformer havmg a' core of magneticmaterial,

that for measured values below a point in balanced opposing portions, atransformer v having a core of magnetic material, and primary andsecondary windings having approximately the same number of turns, saidtransformer primary and one ortion of said 76 instrument winding inseries eing connected to said alternating-current circuit, saidtransformer seconda being connected to the other portion of saidinstrument winding.

6. In combination with an alternatingcurrent system, a suppressed zerovoltmeter comprising an electrical instrument having a winding dividedinto two substantially balanced opposing portions, a transformer havinga core of magnetic material, and primary and secondary windings havingsubstantially the same number of turns, said transformer primary and oneportion of said instru-' ment winding in series being connected to saidalternating-current system, said transformer winding being connected tothe other portion of said instrument winding, the relationship betweenthe electrical and magneticcircuits of the transformer being such 0 thelower portion of the scale range of the voltmeter the transformer coreis relatively unsaturated and for measured values within the range ofthe voltmeter, the transformer core becomes saturated. In witnesswhereof, I have hereunto set my hand.

BY PION W. ST. CLAIR.

' and primary and secondary windings, said transformer primary and oneof said field windings in series being connected across saidalternating-current system, said transformer secondary being connectedto the other of said field windings, the relationship 55 between theelectrical and magnetic circuits of the transformer being such that formeasured values below a point in the lower portion of the range of thevoltmeter the transformer core is relatively unsaturated and for 60measured values within the range of the voltmeter, the transformer corebecomes saturat- In combination with an alternatingcurrent circuit, anelectrical instrument having a winding divided into two substantially

